R help - Apr 2011 - Correlation Matrix

Listers,

I have a question regarding correlation matrices. It is fairly straight
forward to build a correlation matrix of an entire data frame. I simply use
the command cor(MyDataFrame). However, what I would like to do is construct
a smaller correlation matrix using just three of the variable out of my data
set.

When I run this:
cor(MyDataFrame$variable1, MyDataFrame$variable2,MyDataFrame$variable3) I
get an error.

Is there a way to do this through a built in function or is this something I
have to construct manually?

Thanks

	[[alternative HTML version deleted]]

Hi Dmitry,

You might try

with(MyDataFrame[, 1:3])

is variable1, variable2 and variable3 correspond to the first three columns
of your data, or

with( MyDataFrame( cor( cbind( variable1, variable2, variable3) ) ) )

otherwise.

HTH,
Jorge



On Thu, Apr 7, 2011 at 3:09 PM, Dmitry Berman <> wrote:
> Listers,
>
> I have a question regarding correlation matrices. It is fairly straight
> forward to build a correlation matrix of an entire data frame. I simply use
> the command cor(MyDataFrame). However, what I would like to do is construct
> a smaller correlation matrix using just three of the variable out of my
> data
> set.
>
> When I run this:
> cor(MyDataFrame$variable1, MyDataFrame$variable2,MyDataFrame$variable3) I
> get an error.
>
> Is there a way to do this through a built in function or is this something
> I
> have to construct manually?
>
> Thanks
>
>        [[alternative HTML version deleted]]
>
> ______________________________________________
> R-help@r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>
	[[alternative HTML version deleted]]

On 7 April 2011 12:09, Dmitry Berman <ravenblur at gmail.com>
wrote:
> Listers,
>
> I have a question regarding correlation matrices. It is fairly straight
> forward to build a correlation matrix of an entire data frame. I simply use
> the command cor(MyDataFrame). However, what I would like to do is construct
> a smaller correlation matrix using just three of the variable out of my
data
> set.
>
> When I run this:
> cor(MyDataFrame$variable1, MyDataFrame$variable2,MyDataFrame$variable3) I
> get an error.
>
> Is there a way to do this through a built in function or is this something
I
> have to construct manually?
>

You can use cbind().

cor(cbind(MyDataFrame$variable1, MyDataFrame$variable2,MyDataFrame$variable3) )

Jeremy

On Apr 7, 2011, at 3:09 PM, Dmitry Berman wrote:
> Listers,
>
> I have a question regarding correlation matrices. It is fairly  
> straight
> forward to build a correlation matrix of an entire data frame. I  
> simply use
> the command cor(MyDataFrame). However, what I would like to do is  
> construct
> a smaller correlation matrix using just three of the variable out of  
> my data
> set.
>
> When I run this:
> cor(MyDataFrame$variable1, MyDataFrame$variable2,MyDataFrame 
> $variable3) I
> get an error.
But you choose not to offer it. Why is that?
>
> Is there a way to do this through a built in function or is this  
> something I
> have to construct manually?
Neither. You need to learn how R does argument matching:

 From help(cor)
"Usage:
cor(x, y = NULL, use = "everything", method = c("pearson",
"kendall",
"spearman"))"

So your 3 unnamed arguments were matched by position to `x`, `y` and  
`use`.
Try cor(x = myDataFrame[, c("variable1", "variable2",
"variable3")]

-- 

David Winsemius, MD
West Hartford, CT